Quantum limited heat flow and heat Coulomb blockade in a ballistic quantum channel

Quantum physics predicts that there is a fundamental maximum heat conductance across a single transport channel, and that this thermal conductance quantum GQ is universal, independent of the type of particles carrying the heat. However, the behaviour of electrons in small electronic circuits is dictated by both Coulomb interactions and quantum mechanics. Using sensitive noise thermometry at very low temperatures, we are able to measure the thermal conductance quantum in a ballistic electron channel. At the lowest temperatures we also observe that, when a small metallic circuit node is connected to several channels, inter-channel correlations suppresses exactly one thermal conductance quantum, whereas the electrical conductance is unchanged, demonstrating a large departure from the Wiedemann-Franz law paradigm. This finding establishes the different nature of the quantum laws for thermal transport in nanocircuits.